Add more descriptive error message in the presence of OpenAI API timeouts

[jackgerrits]

Why are these changes needed?

API timeouts can be confusing to a user. This adds a more descriptive error message when they occur and offers a suggestion to mitigate.

Related issue number

Checks

• I've included any doc changes needed for https://microsoft.github.io/autogen/. See https://microsoft.github.io/autogen/docs/Contribute#documentation to build and test documentation locally.
• I've added tests (if relevant) corresponding to the changes introduced in this PR.
• I've made sure all auto checks have passed.

[codecov-commenter]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (8ece258) 35.26% compared to head (5912087) 47.04%.

Files	Patch %	Lines
autogen/oai/client.py	20.00%	4 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1577       +/-   ##
===========================================
+ Coverage   35.26%   47.04%   +11.78%     
===========================================
  Files          44       44               
  Lines        5323     5327        +4     
  Branches     1234     1305       +71     
===========================================
+ Hits         1877     2506      +629     
+ Misses       3292     2610      -682     
- Partials      154      211       +57     

Flag	Coverage Δ
unittests	47.00% <20.00%> (+11.74%)	⬆️

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[sonichi]

Suggested a modification to consider different use cases.